A closed system has been recently used in medicine, to prevent the contained solution, such as infusion therapy, from contact with the atmosphere. Configuration and materials of the container for medical solution for a closed injection system must be considered such that it is soft enough to drain the contained solution with gravity pressure. This kind of solution container also must be able to endure autoclave sterilization for the contained solution.
Further, the container is preferably made of transparent material so that the level of the solution can be checked easily and particle matter can be inspected from the outside. In order to obtain these objectives, soft polyvinyl chloride or ethylene-vinyl acetate copolymer have been extensively utilized as the materials of the conventional solution container. Soft polyvinyl chloride poses a health problem for human body, where a great amount of plasticizer may dissolve into the contained solution. On the other hand, ethylene-vinyl acetate copolymer may dissolve into the contained solution as the result of deacetating at forming, and does not have any heat-resistance during autoclave sterilization.
Therefore, ethylene-vinyl acetate copolymer must be cross-linked by radiation such as gamma ray in order to get specified heat-resistance, which causes an additional process in producing containers. In addition to this, the radiation decomposes ethylene-vinyl acetate copolymer to produce organic substances such as acetone, acetaldehyde, acetic acid, isobutane, n-butane, butadiene, propylene etc., and therefore air ventilation is required to exhaust these organic substances, which adds an additional process in producing containers and makes it difficult to keep the work area safe.
Polyolefin, polyamide, polyurethane etc., being much safer to use and having superior properties, have been considered for the materials of containers for medical solution, especially polyolefin has been seen as the most adequate one because of its low price. However, it was extremely difficult to produce a desired container for medical solution with these materials; polyolefin, polyamide, polyurethane etc. As polyolefin, polyamide and polyurethane have lower dielectric loss than polyvinyl chloride or ethylene-vinyl acetate copolymer, high frequency electric fields do not produce enough heat to dissolve the material, thereby these polymers are not available for high frequency sealing as in the case of polyvinyl chloride. Accordingly, for example, when a container for medical solution is made of polyolefin tube which is produced by inflation forming, or is made of two pieces of polyolefin sheet, the open end of the tube itself or the specified part covered with an additional sheet must be welded by impulse sealing or heat sealing. However, it is difficult to weld complicated structures with impulse sealing, in contrast to high frequency sealing, and also difficult to weld the materials with different thickness, on the surface of structures such as pipes, because impulse sealing and heat sealing induce heat to the materials from the outside, thus these ways of sealing make it difficult to form a small port on the top of a container for medical solution.
On the other hand, blow molding containers for medical solution made from polyolefin may be considered, in which the small port portion is integral with the body portion. However, the container for medical solution made by this method has the problem where the contained solution can not be completely drained, because the material is not soft enough, the body portion is cylindrical, the wall thickness of the body portion is almost uniform, and the wall thickness of the body near the peripheral area in tail end is greater than the center portion. Therefore, the container for medical solution made by the conventional blow molding is not available for a closed system. No container for medical solution suitable for containers for infusion fluid or the like has been developed until now by these methods.
The object of this invention is to provide a new container for medical solution and the method of making the same.
Another object of this invention is to also provide a container for medical solution made from organic polymers, suitable for containers for infusion fluid or the like, and the method of making the same.
Further object of this invention is to provide a container for medical solution made from organic polymers, which can drain the contained solution easily and completely, and the method of making the same.